1. Field of the Invention
The present invention relates to a photosensitive material exposure apparatus, which records an image on the photsensitive material by main-scanning the image by an exposure device, while sub-scanning the photosensitive material by using an exposure drum or plurality of exposure rollers which are driven and rotated by driving force of a driving device.
2. Description of the Related Art
Conventionally, in a case in which an image is recorded on a photosensitive planographic printing plate such as a PS (presensitized) plate, exposure is carried out in a state in which a lithographic film is superposed on top of the photosensitive planographic printing plate.
An image is recorded on the lithographic film by a photosensitive material exposure apparatus which is called a `film setter`, and through a developing process, the image is formed.
A magazine that takes up and accommodates therein an elongated lithographic film in layers is set in this film setter.
The lithographic film that is pulled out from this magazine is wound around an exposure drum. At this time, nip rollers are disposed at two different points on the circumference of the exposure drum. The lithographic film is nipped between the nip rollers and the exposure drum. A predetermined length of the lithographic film is kept in close contact with a portion of a circumferential surface of the exposure drum. The exposure drum is rotated at a predetermined rotational speed by a driving force of a driving device, and this rotation is a sub-scanning movement. An image recording apparatus, which is an exposure device, is disposed in a radial direction of the circumferential surface of the exposure drum, at which the lithographic film is kept in close contact.
In the image recording apparatus, light beams emitted from a laser are scanned in an axial direction of the exposure drum through a plurality of optical systems (main-scanning). Accordingly, main-scanning is carried out repeatedly with the light beams while the lithographic film is sub-scanned. Because the light beams are controlled to be on/off (or duty-controlled) on the basis of image information, a predetermined image can be recorded on the lithographic film.
The lithographic film on which images have been recorded is guided to an ordinary conveying path, is discharged from the film setter, and then is fed to a developer for the next process.
In a case in which a printed material produced by using a photosensitive planographic printing plate is a color image, a photosensitive planographic printing plate must be prepared for each of four color components of C (cyan), M (magenta), Y (yellow), and K (black) with respect to each image (i.e., four photosensitive planographic printing plates).
In positioning these four photosensitive planographic printing plates relatively with each other, a main-scanning starting line on the lithographic film must be positioned accurately. For this reason, holes for positioning these four photosensitive planographic printing plates are punched previously in the lithographic film such that the lithographic film and each of the photosensitive planographic printing plates are superposed relatively to each other on the basis of these punched holes.
In recent years, there has been provided a photosensitive material exposure apparatus which records an image directly on the photosensitive planographic printing plates by using an exposure device. In this case, holes for positioning these photosensitive planographic printing plates to allow the plates to be wound accurately around a printer drum must be punched. When the image is printed, each of the photosensitive planographic printing plates is wound around the printer drum on the basis of the holes punched in the four photosensitive planographic printing plates.
A punching unit for punching these holes is built into the film setter.
However, if the photosensitive material is slackened inside the photosensitive material exposure apparatus during the conveyance thereof, the punched holes and the main-scanning starting line on the photosensitive material may displace from each other by an amount corresponding to the slack. Therefore, in order to have a hole-punching position and a main-scanning starting line position correspond relatively to each other on the photosensitive material in the photosensitive material exposure apparatus, a complicated positioning control becomes necessary.